State-of-the-art hydromechanical transmissions, such as utilized in modern military tanks, are equipped with automatic (electronic) ratio controllers acting to adjustably vary the displacements (strokes) of the hydraulic pumps in the transmission hydrostatic pump/motor drive units to achieve vehicle propulsion at speeds requested by the operator. Thus, the operator has no direct control over pump stroke, i.e., transmission ratio. In the event of a loss of electrical power or a failure of the automatic ratio controller, the vehicle is immobilized, even though its engine remains running.
It is accordingly an object of the present invention to provide method and apparatus for retaining vehicle mobility despite failure of the electrical/electronic controller for the vehicle's hydromechanical transmission.
An additional object is to provide apparatus of the above-character for manually overriding the automatic ratio controller in a hydromechanical transmission such as accommodate direct operator control of pump stroke in the transmission hydrostatic drive units.
A further object is to provide manual override apparatus of the above-character, wherein the conversion from automatic to manual control of pump stroke is achieved in an expeditious and safe manner.
Another object is to provide manual override apparatus of the above-character, which can be readily implemented in hydromechanical transmissions without disturbing the automatic ratio controller interface.
Yet another object is to provide manual override apparatus of the above character, wherein the operator control interface is simple and convenient to use.
Other objects of the invention will in part be obvious and in part appear hereinafter.